Nanoscale organization is the key issue for operation of molecular opto-electronic devices based on supramolecular structures, nanoparticles and polymers. Properties of these complex systems are determined not only by their chemical composition but mostly by their organization and environment at nano-meter scale. Single Molecule Spectroscopy (SMS) allows unravelling individual properties of nano-objects usually hidden by sample heterogeneity. In our group we apply SMS to such multi-chromophoric nano-objects as conjugated polymers (organic semiconductors), dendrimers, natural light-harvesting complexes, J-aggregates of organic dyes and organic dye assemblies on surfaces of carbon nanotubes. All these systems have many chromophores organized in a specific way allowing for efficient energy exchange. We study energy migration, excited state dynamics, triplet and charged state generation and influence of internal organization of chromophores and environment on these processes. Understanding these fundamental issues is of a great importance for applications of such materials as light collectors and emitters, charge conductors and molecular recognitions tools. In our group we have developed a novel SMS method called "2D polarization single molecule imaging". It allows monitoring topology of a nano-object and energy transfer between the initially excited and finally emitting entities (chromophores).